Alright, this is a odd problem that I've never seen with what is probably a obvious solution.
I just built a new desktop last night. i5 4690k, GTX 970, 8gb, etc etc with this power supply: http://www.newegg.com/Product/Product.aspx?Item=N82E16817438028
Tonight I decided to do the software stuff and some OCing (Well, I have the ASRock Extreme3 board and used a OC preset - 4.4ghz). All went well, temps stable and the such. Now, I'm not sure if this is relevant information but this is when the fail happened. My MB only came with two sata cables, and I had one run to my HDD and another to my DVD drive. I finished using my DVD drive for the time being and wanted to run a SSD, so I shut down my computer, switched the sata cable, and tried to power my PC - except it wouldn't turn on.
So I sat there frantically troubleshooting to find that there was ONE way to turn my PC on - to plug the 24pin connector into EVGA's diagnostic tool, and then directly into my 24pin connector on the MB, and then hit the power button. Turns on, works fine. I can restart as well and it works well. No error issues of any kind.I can even shut my PC off and hit the power button and it works then.
What in the world is going on here that my power-supply needs a "kick-start" from the diagnostic tool?